Qualification of Concrete Workability by Means of the Vibrating Slope Apparatus

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Abstract

A new device, the Vibrating Slope Apparatus (VSA), developed for qualifying concrete workability under vibration, was borrowed by the International Center for Aggregates Research (ICAR) Project 105 researchers for evaluation. Initial evaluation consisted of testing 24 different concretes that possessed a wide range of workability. The results indicate that the VSA is capable of differentiating between mixtures of similar workability and characterizing established trends. However, testing identified three problems inherent of the proposed test method. An excessive amount of time required to obtain results, the possibility of shear failure of a sample that skews results, and the possibility of an inverse relationship, if the minimum of two chute angles are tested. To solve these problems, the VSA was fitted with an accelerometer to monitor vibration displacement and frequency during testing. A new wedged-shape chute gate was also constructed. The data from the accelerometer were consolidated into one variable, energy, which was used to replace the chute angle from the initial test procedure. The new equipment and procedure were evaluated in a similar manner as before and promising results were obtained. The new procedure solved all three problems identified with the original procedure. A linear correlation between VSA and slump cone measurements for less then 3 inches was defined. This new method was able to characterize expected patterns and differentiate between mixtures of similar workability in an acceptable time, whereas a single-point test, the slump cone, was not. However, the size and complexity of the VSA limit implementation within the field.